For machining process, machine assembling, etc., it is very important to position a work or workpiece which will be processed or assembled.
In an automatic machining process of a work, if a reference point of the work to be processed is not accurately grasped relative to an origin point of a machine tool, the work could not be accurately machine-processed. In automatic machine assembling, on the other hand, it is technically possible to provide a work to be assembled a reference plane or the like so that an assembling device detects this point and also provide a position adjusting mechanism for adjusting an assembling position. However, it requires costs and detection time, resulting in a long lead time.
In view of such problems, techniques as described in Patent Literatures 1 to 4 have been proposed.
Patent Literature 1 discloses a technique of automatically changing the position of a knock pin.
Some process lines would be used to feed a plurality of kinds of works to be processed. It is ideal to provide a machining line per kind of work; however, it does not worth the cost for a small number of lots, and therefore one line is sometimes used for processing a plurality of kinds of works. In this case, positioning has to be changed according to the kinds of works.
In Patent Literature 1, two works of different kinds are formed respectively with knock holes to be used for positioning. Assuming that one of knock pins provided in a positioning device is referred to as a main knock pin and the other is referred to as an auxiliary knock pin, the position of the auxiliary knock pin is slidable with respect to the main knock pin according to the work. Since the auxiliary knock pin is moveable to two positions, it can correspond to a knock hole of each work.
Patent Literature 2 discloses a technique related to a jig plate of a reference base.
The jig plate is formed with a plurality of knock pin holes and vertical and lateral grooves and provided with a block that is slidable in the grooves and has a knock pin hole. In this technique, one knock pin inserted into one knock hole formed in the work is inserted into one of the knock pin holes of the jig plate and the other knock pin inserted into the other knock hole of the work is inserted into the knock pin hole of the block to determine the position of a work.
When the kind of a work is changed, having a different pitch between one knock hole and the other knock hole, the knock pin is slid to move within the grooves of the jig plate, thereby changing a pitch between one knock pin and the other knock pin to correspond to a hole-to-hole pitch of the work.
Thus, the positioning of works having different pitches can be performed.
Patent Literature 3 discloses a technique related to a temporary work clamping device.
A clamping system is arranged such that a main clamp and an auxiliary clamp are coupled with a connecting rod to clamp a work with a time lag. The main clamp and the auxiliary clamp are coupled with the connecting rod and a single drive source is secured in a position off the center of the connecting rod. It is therefore possible to fix a work by the main clamp first and then by the auxiliary clamp so that the location of the work is fixed by the main clamp. Thus, clamping can be achieved without causing displacement of the work.
Patent Literature 4 discloses a technique related to a positioning and fixing device for a knock pin.
This technique is to position a work with two knock pins. Depending on different works, one knock pin is slidable in a long hole and is positioned in place by a clamping mechanism utilizing the principle of leverage and the other knock pin is slidable in a long hole formed at an angle so that its extension line intersects with that of the former long hole and is positioned in place by the clamping mechanism.
This configuration allows the positioning of works of which positioning holes are arranged at different pitches.
However, the techniques disclosed in Patent Literatures 1 to 4 may have a problem with difficulty in improving the positioning accuracy.
In the case where two knock pins are basically used for positioning, the knock holes formed in each work are designed with some degree of clearance.
As to the knock holes to be formed in a work, if using a technique of processing a block material, the diameter of each knock hole and a hole-to-hole pitch can be determined with significant accuracy. However, works made of steel plate or cast metal have large accuracy tolerances in the knock hole diameter and the hole-to-hole pitch. Furthermore, even machining process needs much time for accurate process and can only provide accuracy in line with costs.
Such work positioning requires determination of the position and the kind of knock pins to absorb errors in knock hole diameter and hole-to-hole-to-hole pitch.
Even when the diameter and the hole-to-hole pitch of the knock holes formed in the work can be formed with high machining accuracy, some degree of clearance is needed to facilitate insertion/removal of the work with respect to the knock pin.
When the work is inserted on the knock pin, conceivably, the work could be inclined. Unless the clearance between the knock pin and the knock hole is determined not to allow this inclination, it is very difficult to insert/remove the work with respect to the knock pin.
From such reason, the diameter of the knock pin is determined to be narrower to some extent than the diameter of the knock hole formed in the work. Thus, the positioning accuracy will lower by just that much.
According to the positioning method using the knock pin and the clamp in Patent Literatures 1 to 4 in which the auxiliary positioning means is moved with respect to the main positioning means, it is conceivable that the hole-to-hole pitch can be determined roughly. However, as long as it is configured to insert the knock pin in the knock hole, the clearance has to be provided as ever for insertion.
However, providing the clearance in the diameter of the knock pin with respect to the diameter of the knock hole indicates that a work positioning error is permitted by the clearance. By just this clearance, positional displacement is caused in a direction that rotates about the main knock pin.
To solve such problem, Patent Literature 5 discloses a technique related to a positioning device and a clamping system including it.
FIG. 19 is a vertical sectional view of an auxiliary knock pin 100 in Patent Literature 5. FIG. 20 is a horizontal sectional view of the auxiliary knock pin 100 in Patent Literature 5.
The auxiliary knock pin 100 includes a plug member 110 at a leading end of a housing 109. The plug member 110 is formed with a slide outer surface 110a. A slide part 111 formed with a slide surface 111a which contacts with the slide outer surface 110a is placed in contact with the inner surface of a cylindrical wedge member 113. The wedge member 113 contacts with the inner surface of an engagement member 114 held in a cap member 112.
The auxiliary knock pin 100 is configured as above. Accordingly, when the cap member 112 is inserted into an auxiliary knock hole of a work, the slide surface 111a of the slide part 111 and the slide outer surface 110a of the plug member 110 are slid and moved in parallel to move the cap member 112 with respect to the housing 109. This corrects a pitch error between the main knock hole and the auxiliary knock hole formed in the work.
Furthermore, the cap member 112 is connected to a piston 115. When the piston 115 is moved down from a state in FIG. 19 by hydraulic pressure, the engagement member 114 is expanded in diameter because of the wedge shape of the wedge member 113, thereby eliminating the clearance between the auxiliary knock hole and the cap member 112.
This Patent Literature 5 is also a technique of basically positioning a work with two knock pins and having a function of absorbing the pitch error between the main knock hole and the auxiliary knock hole.
According to a processing machine using such positioning device, therefore, it is possible to accurately process a work with reference to the main knock hole.    Patent Literature 1: JP examined patent publication No. 4(1992)-20739    Patent Literature 2: JP examined utility model publication No. 6(1994)-44586    Patent Literature 3: JP unexamined patent publication No. 9(1997)-103928    Patent Literature 4: JP unexamined patent publication No. 2002-263977    Patent Literature 5: Pamphlet of WO2005/037485A1